Kaposi's sarcoma-associated herpesvirus (KSHV) is etiologically associated in the pathogenesis of Kaposi's sarcoma (KS), an AIDS-defining vascular tumor. Our long term objectives are to examine KSHV infection of endothelial cells and role in KS pathogenesis. To determine the role of lytic replication in KS pathogenesis, we focused on KSHV interactions with cell surface molecules and examined the interactions of KSHV-gB with integrin molecules. We have demonstrated that KSHV interacts with integrins of adherent target cells which overlaps with the induction of pre-existing integrin associated host cell signal pathways, such as FAK, Src, PI3-K, Rho-GTPases, Dia-2, PKC, ERK1/2 and NF-kB pathways that are critical for virus entry, nuclear delivery and initiation of viral gene expression. These novel paradigms in the field of virus-receptor interactions suggest that KSHV interaction with host cell receptors has evolved not to be a mere conduit for viral DNA entry, but has evolved to manipulate the host cell signaling pathways to create an appropriate intracellular environment that is conducive to the establishment of a successful infection. We hypothesize that KSHV interacts with a family of functionally related endothelial cell surface molecules, such as 31, V3/V5 and CD98-xCT, in a sequentially co- coordinated manner to mediate its binding, entry and infection. To test the hypothesis, we have formulated the following four major specific aims. 1. To decipher the temporal sequence of KSHV interactions with endothelial cell surface 31, V3 and V5 integrins, and to determine the role of KSHV-gB disintegrin, gpK8.1A-NGR and gH-SGD motifs in integrin interactions. 2. To decipher KSHV interactions with endothelial CD98/xCT molecules, their associations with integrins, to identify the KSHV envelope glycoproteins involved in the interactions, and to define the interactions of recombinant gpK8.1A deleted KSHV with integrins, CD98 and xCT molecules. 3. To decipher the role of CD98-xCT in KSHV infection of endothelial cells and to define the stage at which CD98-xCT play roles. 4. To decipher the role of integrins, CD98, xCT, ROS and Nrf2 molecules in KSHV induced endothelial cell signal pathways during the early stages of infection. These studies are significant as deciphering the host cell receptors involved in the early stages of KSHV interactions with endothelial cells will lead to a better understanding of KSHV tropism and pathogenesis and to the development of strategies to control KSHV infection associated KS and other diseases. Kaposi's sarcoma-associated herpesvirus (KSHV) or HHV-8 is etiologically associated in the pathogenesis of Kaposi's sarcoma (KS), an AIDS-defining vascular tumor. Our studies suggest that KSHV interacts with a family of functionally related endothelial cell surface molecules not only to mediate the entry of viral DNA into the target cells but also to manipulate the host cell signaling pathways to create an appropriate intracellular environment that is conducive to the establishment of a successful infection. Deciphering the interactions between KSHV and host cell receptors involved in the early stages of infection of endothelial cells will lead to a better understanding of tropism and pathogenesis of KSHV and to the development of strategies to control KSHV infection and associated diseases.